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Lect15-Phys172s11-(8.1-8.8-Energy_quantization)

# Lect15-Phys172s11-(8.1-8.8-Energy_quantization) - PHYS 172...

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Spring 2011 PHYS 172: Modern Mechanics Lecture 15 – Energy Quantization Read 8.1 – 8.8 EXAM 2 is next week Time: 8:00-10:00 pm Wed March 9th Place: Elliott Hall Material: lectures 9-14 (may require previous material as well) Problems: multiple choice, 14 questions (70 points) write-up part, hand graded (30 points) Equation sheet : provided Practice exam: will be posted Note: no lecture on March 10 Quantization •Classical Physics: quantities are continuous. • Quantum Physics: Some quantities are limited to a discrete set of values. Example: charge, Q = N . e

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Energy Levels are quantized for many microscopic systems: Energy of a photon Planck: light is emitted by quanta (1900) Einstein: light consists of quanta! (1905) Planck’s constant: h = 6.6 10 -34 J . s photon Photon energy and wavelength: E light light hc h ν λ = = Visible light Electromagnetic spectrum 400 450 500 550 600 700 750 650 Wavelength nm E = 3.1 eV ν = 7.5 × 10 14 E = 1.8 eV ν = 4.2 × 10 14 Lower energy Higher energy photons
Experimental fact: Atoms have QUANTIZED energy levels. Light from these lamps comes only in a few narrow colors, which means the photons in those lines have a fixed, well-defined energy.

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Lect15-Phys172s11-(8.1-8.8-Energy_quantization) - PHYS 172...

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